This project proposes to analyze by spectrofluorometric methods and fluorescence microscopy, the properties and interactions of various proteins and other macromolecules. Particular emphasis will be focused on studying the effect of binding of ligands to their cell surface receptors in terms of their state of aggregation, lateral mobility and rotational flexibility as well as interactions with other molecules. We will develop new methods for labelling proteins with fluorogenic compounds so that they can be detected, under different conditions, in different states. The use of these spectroscopic methods in protein chemistry will be extended to similar studies at the single cell level.